Synonyms for Dowser (same or very similar meaning)
WordNet sense 1 (someone who uses a divining rod to find underground water):
rhabdomancer, rhabdomancer, water witchWordNet sense 2 (forked stick that is said to dip down to indicate underground water or oil):
waterfinder, divining rod, dowsing rod, water finderFrom the ODE community, based on WordNetadd/edit